Short and long training fields

ABSTRACT

A method includes receiving a first plurality of symbols comprising complex portions. The method further includes applying conjugate symmetry to the first plurality of symbols, producing a second plurality of symbols comprising no complex portions. The method further includes transforming the second plurality of symbols using an inverse fast Fourier transform, producing a third plurality of symbols. The method further includes interpolating the third plurality of symbols, generating a short training field comprising at least one real portion of the third plurality of symbols, generating a long training field comprising at least one real portion of the third plurality of symbols, and transmitting the short training field and long training field in a WPAN.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 14/025,628 filed on Sep. 12, 2013, which is a continuation ofU.S. patent application Ser. No. 12/868,397 (now U.S. Pat. No.8,553,730), filed Aug. 25, 2010, which claims priority to U.S.Provisional Patent Application Nos. 61/238,445, filed on Aug. 31, 2009,and 61/287,586, filed on Dec. 17, 2009, all of which are herebyincorporated herein by reference.

BACKGROUND

Wireless personal area networks (“WPANs”) are used to convey informationover relatively short distances. Unlike wireless local area networks(“WLANs”), WPANs need little or no infrastructure, and WPANS allowsmall, power-efficient, and inexpensive solutions to be implemented fora wide range of devices. Smart Utility Networks (“SUNs”) may operateeither over short ranges such as in a mesh network where utility meterinformation is sent from one utility meter to another or over longerranges such as in a star topology where utility meter information issent to a poletop collection point. The terms WPAN and SUN are usedinterchangeably in this document.

SUMMARY

System and methods for generating short and long training fields forsmart utility networks are described herein. In at least some disclosedembodiments, a method includes receiving a first plurality of symbolscomprising real portions and complex portions. The method furtherincludes applying conjugate symmetry to the first plurality of symbols,thus producing a second plurality of symbols comprising real portionsand no complex portions. The method further includes transforming thesecond plurality of symbols using an inverse fast Fourier transform,thus producing a third plurality of symbols. The method further includesinterpolating the third plurality of symbols, generating a shorttraining field comprising at least one real portion of the thirdplurality of symbols, generating a long training field comprising atleast one real portion of the third plurality of symbols, andtransmitting the short training field and long training field in a WPAN.

In other disclosed embodiments, a device includes a processor, a memorycoupled to the processor, and an antenna coupled to the processor. Theprocessor generates a packet for use in a WPAN comprising a shorttraining field as part of a synchronization header and a long trainingfield as part of the synchronization header.

In yet other disclosed embodiments, a machine-readable storage mediumincludes executable instructions that, when executed, cause one or moreprocessors to generate a packet for use in a WPAN comprising a shorttraining field as part of a synchronization header and a long trainingfield as part of the synchronization header.

These and other features and advantages will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, referenceis now made to the accompanying drawings and detailed description,wherein like reference numerals represent like parts:

FIG. 1 compares peak-to-average power ratios (PAR) in decibels betweenvarious sequences of short training fields (“STFs”) and long trainingfields (“LTFs”) in accordance with various embodiments;

FIG. 2 illustrates an embodiment of a packet containing a STF and LTF inaccordance with various embodiments;

FIGS. 3A-3J illustrate the frequency domain representations ofembodiments of STFs and LTFs generated with different inverse fastFourier transform settings in accordance with various embodiments;

FIG. 4 illustrates generation of STFs and LTFs via modules in accordancewith various embodiments;

FIG. 5 illustrations generation of STFs via modules in accordance withvarious embodiments;

FIG. 6 illustrates negation of last STF to enable boundary detection inaccordance with various embodiments;

FIG. 7 illustrates a method of generating STFs and LTFs in accordancewith various embodiments; and

FIG. 8 illustrates a particular machine suitable for implementing one ormore embodiments described herein.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following claims and descriptionto refer to particular components. As one skilled in the art willappreciate, different entities may refer to a component by differentnames. This document does not intend to distinguish between componentsthat differ in name but not function. In the following discussion and inthe claims, the terms “including” and “comprising” are used in anopen-ended fashion, and thus should be interpreted to mean “including,but not limited to . . . .” Also, the term “couple” or “couples” isintended to mean an optical, wireless, indirect electrical, or directelectrical connection. Thus, if a first device couples to a seconddevice, that connection may be through an indirect electrical connectionvia other devices and connections, through a direct optical connection,etc. Additionally, the term “system” refers to a collection of two ormore hardware components, and may be used to refer to an electronicdevice.

DETAILED DESCRIPTION

The following discussion is directed to various embodiments of theinvention. Although one or more of these embodiments may be preferred,the embodiments disclosed should not be interpreted, or otherwise used,as limiting the scope of the disclosure, including the claims, unlessotherwise specified. In addition, one having ordinary skill in the artwill understand that the following description has broad application,and the discussion of any embodiment is meant only to be exemplary ofthat embodiment, and not intended to intimate that the scope of thedisclosure, including the claims, is limited to that embodiment.

A WPAN or low-rate WPAN is a simple, low-cost communication network thatallows wireless connectivity in applications with limited power andrelaxed throughput requirements. The main objectives of a WPAN are easeof installation, reliable data transfer, short-range operation,extremely low cost, reasonable battery life, and a simple and flexibleprotocol.

Some characteristics of a WPAN are:

-   -   Over-the-air data rates of 250 kb/s, 100 kb/s, 40 kb/s, and 20        kb/s    -   Star or peer-to-peer operation    -   Allocated 16-bit short or 64-bit extended addresses    -   Optional allocation of guaranteed time slots    -   Carrier sense multiple access with collision avoidance channel        access    -   Low power consumption    -   Energy detection    -   Link quality indication    -   16 channels in the 2450 MHz band, 30 channels in the 915 MHz        band, and 3 channels in the 868 MHz band.        These characteristics are not requirements, and each WPAN may        deviate from the characteristics in numerous ways. Two different        device types can participate in a WPAN: a full-function device        (“FFD”) and a reduced-function device (“RFD”). The FFD can        operate in three modes serving as a personal area network        (“PAN”) coordinator or a device. A FFD can talk to RFDs or other        FFDs while a RFD can talk only to a FFD. More information can be        found at IEEE Std. 802.15.4-2006 available at        http://www.ieee802.org/15/pub/TG4.html and hereby incorporated        by reference.

A utility network or smart utility network (“SUN”) is a low-rate (e.g.,40 kbps to 1 Mbps) low-power WPAN that is specifically designed for usein utility metering applications such as transmitting electric, gas,water usage, and other like data from the customer premises to a datacollection point operated by the utility. For example, utility metersare installed for each house in a residential neighborhood, and theusage data is sent periodically from each utility meter to a datacollection point, which is an element of the WPAN. The data collectionpoint is connected by fiber, copper wire, or wireless connection to acentral office that collects all the usage data for a region. Usage datais sent either directly from each utility meter to the collection pointor from utility meter to utility meter until the collection point isreached in a star or network formation, respectively.

This disclosure describes preamble sequences for use in WPAN packetsthat include a short training field (“STF”) and/or a long training field(“LTF”) for the orthogonal frequency division multiplexing (“OFDM”)physical layer (“PHY”). A STF and LTF are a number of bits in a packet,appearing consecutively in a preamble of the packet in at least oneembodiment. In at least one embodiment, the STF has about one quarterthe number of non-zero tones as compared to the LTF in order to generatea 4× repetition within the IFFT length. The STF is used by the receiverfor automatic gain control settling, packet/boundary detection and/orcoarse frequency offset estimation as discussed herein. The LTF is usedfor fine frequency offset estimation, FFT placement, integer frequencyoffset estimation, and/or channel estimation as discussed herein.Applicability is not limited to SUNs; rather, the teachings herein mayapply to any wireless communication system. In other embodiments, theamount and repetition of the STFs and LTFs vary, and the repetitions mayor may not include the cyclic prefix. In the WPAN packets, there are twoor more STF OFDM symbols followed by multiple LTF OFDM symbols, thepacket header, and the packet payload in at least one embodiment. Inother embodiments, the type, order, and number of packet elements vary.

Table 1 illustrates the MCS levels for the 5 options for OFDM blocksize. Option 1 is generated with a 128 point IFFT, Option 2 is generatedwith a 64 point IFFT, and Options 3, 4, and 5 use 32, 16, and 8 pointIFFTs, respectively.

TABLE 1 Modulation and Coding Schemes for 5 IFFT Sizes Number of DataSub-Carriers (NDSC) Option 1 2 3 4 5 MCS 100 48 22 12 4 NCBPS NDBPSNCBPS NDBPS NCBPS NDBPS NCBPS NDBPS NCBPS NDBPS 0 100 12.5 1 100 25 4812 22 5.5 2 100 50 48 24 22 11 12 6 3 100 75 48 36 22 16.5 12 9 4 200100 96 48 44 22 24 12 5 200 125 96 60 44 27.5 24 15 6 96 72 44 33 24 188 6 7 192 96 88 44 48 24 16 8 8 192 120 88 55 48 30 16 10 9 88 66 48 3616 12 NCBPS = number of coded bits per symbol, NDBPS = number of databits per symbol

Table 2 illustrates alternative MCS levels where the number of datasub-carriers are integer multiples of the number of data sub-carriersfor smaller size IFFTs.

TABLE 2 Alternative Modulation and Coding Schemes for 5 IFFT SizesNumber of Data Sub-Carrier (NDSC) Option 1 2 3 4 5 MCS 96 48 24 12 4NCBPS NDBPS Rate NCBPS NDBPS Rate NCBPS NDBPS Rate NCBPS NDBPS RateNCBPS NDBPS Rate 0 24 12 93.75 1 48 24 187.5 24 12 93.75 12 6 46.88 2 9648 375 48 24 187.5 24 12 93.75 12 6 46.88 3 96 72 562.5 48 36 281.25 2418 140.63 12 9 70.31 4 192 96 750 96 48 375 48 24 187.5 24 12 93.75 5192 120 937.5 96 60 468.75 48 30 234.38 24 15 117.19 6 96 72 562.5 48 36281.25 24 18 140.63 8 6 46.88 7 192 96 750 96 48 375 48 24 187.5 16 862.5 8 192 120 937.5 96 60 468.75 48 30 234.38 16 10 78.13 9 96 72 562.548 36 281.25 16 12 93.75

The STFs and LTFs sequences discussed below have low peak-to-averagepower ratios (“PARs”). In addition to providing packets generated usingthese STFs and LTFs with low PARs: 1) ensure that the transmitter willnot be clipped, therefore ensuring a good error vector magnitude (“EVM”)for the preamble and the channel estimation sequence; 2) allow forboosts to the power of the preamble without clipping; and 3) allow forbetter preamble range for increased robustness in the system.

OFDM is a modulation technique that can be used for the physical layerof the SUN. Some examples of complex OFDM LTF sequences are shown below.Option 1 is generated using a 128 point inverse fast Fourier transform(“IFFT”) at the Nyquist rate, Option 2 is generated using a 64 pointIFFT, and Options 3, 4, and 5 are generated using 32, 16, and 8 pointIFFTs, respectively.

LTF_freq(Option-1)=[0, 1,−1, 1,−1, 1, 1,−1,−1, 1,−1, 1, 1, 1, 1,−1, 1,1, 1, 1, 1,−1, 1,−1, 1, −1, 1,−1, 1, 1,−1, 1,−1,−1,−1, 1, 1, 1, 1, 1,1,−1,−1,−1,−1,−1,−1, 1,−1, 1, 1,−1, 1, zeros(1,23), −1, 1,1,−1,−1,−1,−1, 1, 1,−1,−1, 1, 1, 1,−1,−1, 1, 1,−1,−1,−1,−1,−1, 1,1,−1,−1,−1,−1,−1, 1, 1,−1, 1,−1,−1, 1,−1, 1, 1, 1, 1,−1,−1, 1, 1,−1, 1,1,−1, 1, 1].

LTF_freq(Option-2)=[0,1,−1, 1, 1,−1, 1,−1,−1, 1,−1, 1, 1,−1,−1, 1,1,−1,−1,−1,−1,−1, 1,−1,−1,−1, 1, zeros(1,11), −1,−1,−1,−1, 1, 1, 1,−1,1,−1, 1,−1, 1, 1,−1,−1,−1, 1, 1,−1, 1, 1, 1,−1,−1,−1].

LTF_freq(Option-3)=[0, −1,−1, 1,−1, 1, 1,−1,−1, 1, 1,−1,−1, 1,zeros(1,5), 1,−1, 1,−1, 1, 1, 1, 1, 1, 1, 1, 1,−1].

LTF_freq(Option-4)=[0, −1, 1, 1, 1,−1,−1,−1, 0, 1,−1, 1, 1,−1, 1, 1].

LTF_freq(Option-5)=[0, −1, 1,−1, 0, 1, 1, 1].

These sequences are given in Matlab format. For Option 5, the first 0represents the DC tone, which is not used. The next three subcarriersare 1, 2, and 3 with data −1, 1, −1, respectively. The negativesubcarriers −4,−3,−2,−1 have data 0, 1, 1, 1, respectively. In general,if there are N subcarriers, the Matlab subcarrier numbering is 0, 1, 2,3, . . . , (N/2)−1 followed by −(N/2), . . . , −3, −2, −1.

Some examples of complex STF sequences are shown below.

STF_freq(Option-1)=sqrt(104/24)*[0, 0, 0, 0,−1, 0, 0, 0,−1, 0, 0, 0, 1,0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,−1, 0, 0, 0,−1, 0, 0, 0, 1, 0, 0, 0,−1,0, 0, 0, 1, 0, 0, 0,−1, 0, 0, 0, 1, 0, 0, 0,−1, 0, 0, 0, 0, 0, 0, 0, 0,0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,−1, 0, 0, 0,−1, 0, 0, 0,−1,0, 0, 0,−1, 0, 0, 0,−1, 0, 0, 0,−1, 0, 0, 0,−1, 0, 0, 0, 1, 0, 0, 0, 1,0, 0, 0,−1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,−1, 0, 0, 0].

STF_freq(Option-2)=sqrt(52/12)*[0, 0, 0, 0, 1, 0, 0, 0,−1, 0, 0, 0, 1,0, 0, 0, 1, 0, 0, 0,−1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,0, 0, 0,−1, 0, 0, 0,−1, 0, 0, 0,−1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1,0, 0, 0].

STF_freq(Option-3)=sqrt(26/6)*[0, 0, 0, 0,−1, 0, 0, 0, 1, 0, 0, 0,−1, 0,0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0].

STF_freq(Option-4)=sqrt(14/6)*[0, 0,−1, 0, 1, 0,−1, 0, 0, 0, 1, 0, 1, 0,1, 0].

STF_freq(Option-5)=sqrt(6/2)*[0, 0,−1, 0, 0, 0, 1, 0].

Using these sequences, PAR can be reduced significantly as shown in theexample of FIG. 1. Specifically, the first column identifies the LTF andSTF sequences. The second column identifies the IFFT options used. Thethird column lists the PAR for communication without STFs or LTFsoptimized for PAR. The fourth column lists the PAR for communicationusing optimized STFs and LTFs. The fifth column lists the PAR forcommunication using quadrature phase shift keying (“QPSK”) modulation.

Some examples of alternative LTF sequences are shown below. Thesesequences are given in Matlab format. For Option 5, the first 0represents the DC tone, which is not used. The next three subcarriersare 1, 2, and 3. In general, if there are N subcarriers, the Matlabsubcarrier numbering is 0, 1, 2, 3, . . . , (N/2)−1 followed by −(N/2),. . . , −3, −2, −1.

LTF alternatives for option 4:

ltfr4 = 0 −1 −1 1 −1 −1 1 −1 0 1 1 1 −1 −1 −1 1 ltfr4 = 0 −1 1 1 1 −1 −1−1 0 1 −1 1 1 −1 1 1 ltfr4 = 0 1 −1 −1 −1 1 1 1 0 −1 1 −1 −1 1 −1 −1ltfr4 = 0 1 1 −1 1 1 −1 1 0 −1 −1 −1 1 1 1 −1.

LTF alternatives for option 5:

ltfr5 = 0 −1 −1 −1 0 1 −1 1 ltfr5 = 0 −1 1 −1 0 1 1 1 ltfr5 = 0 1 −1 1 0−1 −1 −1 ltfr5 = 0 1 1 1 0 −1 1 −1 ltfr5 = 0 −1 −1 −1 −1 1 1 −1 ltfr5 =0 −1 1 −1 1 1 −1 −1 ltfr5 = 0 1 −1 1 −1 −1 1 1 ltfr5 = 0 1 1 1 1 −1 −11.

Some examples of alternative STF sequences are shown below. Thesesequences are given in Matlab format. For Option 5, the first 0represents the DC tone, which is not used. The next three subcarriersare 1, 2, and 3. In general, if there are N subcarriers, the Matlabsubcarrier numbering is 0, 1, 2, 3, . . . , (N/2)−1 followed by −(N/2),. . . , −3, −2, −1.

STF alternatives for option 2:

stfr2 = 0 0 0 0 −1 0 0 0 −1 0 0 0 −1 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 00 0 0 0 0 0 0 0 0 −1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 1 0 0 0 −1 0 0 0stfr2 = 0 0 0 0 −1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 1 0 0 0 −1 0 0 0 0 00 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 −1 0 0 0stfr2 = 0 0 0 0 1 0 0 0 −1 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 1 0 0 0 0 0 00 0 0 0 0 0 0 0 0 −1 0 0 0 −1 0 0 0 −1 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0stfr2 = 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 −1 0 0 0 0 0 00 0 0 0 0 0 0 0 0 1 0 0 0 −1 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 1 0 0 0.STF alternatives for option 3:

stfr3 = 0 0 0 0 −1 0 0 0 −1 0 0 0 −1 0 0 0 0 0 0 0 1 0 0 0 −1 0 0 0 1 00 0 stfr3 = 0 0 0 0 −1 0 0 0 1 0 0 0 −1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 10 0 0 stfr3 = 0 0 0 0 1 0 0 0 −1 0 0 0 1 0 0 0 0 0 0 0 −1 0 0 0 −1 0 0 0−1 0 0 0 stfr3 = 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 −1 0 0 0 1 0 00 −1 0 0 0.STF alternatives for option 4:

stfr4 = 0 0 −1 0 −1 0 −1 0 0 0 1 0 −1 0 1 0 stfr4 = 0 0 −1 0 1 0 −1 0 00 1 0 1 0 1 0 stfr4 = 0 0 1 0 −1 0 1 0 0 0 −1 0 −1 0 −1 0 stfr4 = 0 0 10 1 0 1 0 0 0 −1 0 1 0 −1 0.STF alternatives for option 5:

stfr5 = 0 0 −1 0 0 0 −1 0 stfr5 = 0 0 −1 0 0 0 1 0 stfr5 = 0 0 1 0 0 0−1 0 stfr5 = 0 0 1 0 0 0 1 0.

FIG. 2 illustrates a packet format using STFs and LTFs in at least oneembodiment. A synchronization header (“SHR”) comprises a STF and LTF. Asillustrated, the STF and LTF are four and two symbols long respectively,but each can be any size in various embodiments. The STF allows a deviceto perform automatic gain control (“AGC”), packet detection,de-assertion of clear channel assessment (“CCA”) based on CCA modes (CCAMode 1, 2, or 3), and coarse synchronization. The LTF allows a device toperform fine synchronization and perform channel estimation. The packetheader (“PHR”) can be any number of data symbols or bits “M.” In atleast one embodiment, the PHR contains:

-   -   A Rate field specifying the data rate of the payload frame (5        bits);    -   One reserved bit after the Rate field;    -   A Frame Length field specifying the length of the payload (11        bits);    -   Two reserved bits after the Frame Length field;    -   A Scrambler field specifying the scrambling seed (2 bits);    -   One reserved bit after the Scrambler field;    -   A Header Check Sequence (“HCS”) 8-bit CRC taken over the data        fields only; and    -   Six tail bits, which are all zeros, for Viterbi decoder        flushing.

The PHR is encoded at the lowest data rate supported for each bandwidthoption in at least one embodiment. The physical layer convergenceprotocol service data unit (“PSDU”), which can be any number of datasymbols or bits “N,” carries a media access control (“MAC”) sublayerframe, which comprises a MAC header, MAC payload, and MAC cyclicredundancy check (“CRC”) in at least one embodiment. The PSDU alsocarries convolutional encoder tail-bits, which can be six zeros, andpad-bits to extend the data to fill an integer number of OFDM symbols.

For OFDM, the STF and LTF fields comprise the preamble. Variousembodiments for the STF and LTF for the five options are defined byFIGS. 3A-3J. These figures correspond to the Improved Complex Sequencecolumn in FIG. 1. FIG. 3A shows the frequency domain representation ofthe STF for Option 1. The scaling factor used in the figure issqrt(104/12). However, various scaling factors are used in various otherembodiments, and the scaling factor can be changed to obtain a desiredsignal level FIG. 3B shows the frequency domain representation of theSTF for Option 2. The scaling factor used in the figure is sqrt(52/12).FIG. 3C shows the frequency domain representation of the STF for Option3. The scaling factor used in the figure is sqrt(26/6). FIG. 3D showsthe frequency domain representation of the STF for Option 4. The scalingfactor used in the figure is sqrt(14/6). FIG. 3E shows the frequencydomain representation of the STF for Option 5. The scaling factor usedin the figure is sqrt(6/2).

LTFs for the five scalable bandwidth OFDM options are defined in FIGS.3F-3J. FIG. 3F shows the frequency domain representation of the LTF forOption 1. FIG. 3G shows the frequency domain representation of the LTFfor Option 2. Similarly, FIGS. 3H-I show the frequency domainrepresentations of the LTFs for Options 3-5.

FIG. 4 illustrates modules 400 or logic in a device for receiving,generating, and transmitting the STFs and LTFs. The device sends andreceives packets in a WPAN as part of a SUN in at least one embodiment.The device preferably comprises a processor, an antenna coupled to theprocessor, and memory coupled to the processor. At 402, packets arereceived, and the packets contain data symbols that may be binary phaseshift keyed (“BPSK”) (−1−j and 1+j), rotated BPSK (−1 and 1), QPSK(−1−j, −1+j, 1−j, and 1+j), or rotated QPSK (−1, 1, −j, and j).

At 404, conjugate symmetry may be applied to the symbols in thefrequency domain, thus producing a real signal in the time domain (i.e.no complex portion to the signal). At a transmitter, this real sequenceonly requires one digital to analog converter (“DAC”) because there isno complex portion to be processed. DCM can also be used for the headerto provide frequency diversity. In an alternative embodiment, a complexmodule or logic is turned off or run at reduced power, and the totalpower necessary to operate the device is reduced. In an alternativeembodiment, the conjugate symmetry may be omitted so that a complex STFand LTF is produced.

At 406, the IFFT converts the symbols to a time domain sequence. In atleast one embodiment, the STF and LTF can be generated offline using theIFFT to form time domain sequences, and these can be stored and used inthe device. The Time-Domain STF for Option-n (n=1,2,3,4,5) is obtainedas follows:

STF_time(Option-n)=IFFT(STF_freq(Option-n)).

The time-domain STF is repeated to fill four OFDM symbols with the last1/4 symbol repetition negated before transmission in at least oneembodiment. In other embodiments, the size of the STF and the size ofthe negated portion vary.

The Time-Domain LTF for Option-n (n=1,2,3,4,5) is obtained as follows:

LTF_time(Option-n)=IFFT(LTF_freq(Option-n)).

In at least one embodiment, the time-domain LTF is repeated to fill twoOFDM symbols before transmission. In other embodiments, the size of theLTF varies.

At 408, frequency domain interpolation is performed by inserting extrazeros after the positive sub-carriers. Alternatively, a time-domaininterpolator can be used to generate an oversampled signal at atransmitter. The interpolation is part of the IFFT in at least oneembodiment. At 410, a DAC converts signals from digital to analog inpreparation for transmittal. In another embodiment, as shown in FIG. 5,the last repetition in the STF is negated at 507. Specifically, the STFcomprises a group of bits that are repeated. In such an embodiment, thelast group of bits is negated.

The receiving device implements a correlator to search for the preamblein at least one embodiment. The correlation is performed using the knowntransmitted preamble at the device. In another embodiment, the deviceperforms a delayed correlation by storing the received signal in memory,and correlating a delayed version of the preamble with a non-delayedversion. For example, if the preamble repeats every 128 samples, thenthe delay can be set to 128 samples. In addition, the phase rotation atthe peak correlation provides an estimate of the carrier-frequencyoffset.

For each of the 5 options, both a short and long training field can bedefined. For Option 5 with an IFFT size of 8, the STF can be defined inthe frequency domain as:

[0 0 −1 0 0 0 −1 0].

The corresponding sub-carriers are given below.

DC 1 2 3 −4 −3 −2 −1.

Applying the IFFT results in:

[−0.2500   0  0.2500   0  −0.2500   0  0.2500   0].

At the transmitter, interpolation occurs to at least four times thesample rate in at least one embodiment. This interpolation can occur aspart of the IFFT or after the IFFT. For example, 24 zeros are insertedafter the highest positive frequency before taking the IFFT as shownbelow.

4*IFFT([0 0 −1 0 zeros(1,24) 0 0 −1 0 ] =[−0.2500 −0.2310 −0.1768 −0.0957 0 0.09570.1768 0.2310 0.2500 0.2310 0.1768 0.09570 −0.0957 −0.1768 −0.2310 −0.2500 −0.2310−0.1768 −0.0957 0 0.0957 0.1768 0.23100.2500 0.2310 0.1768 0.0957 0 −0.0957 −0.1768 −0.2310].

These sequences are given in Matlab format. For Option 5, the first 0represents the DC tone, which is not used. The next three subcarriersare 1, 2, and 3. In general, if there are N subcarriers, the Matlabsubcarrier numbering is 0, 1, 2, 3, . . . , (N/2)−1 followed by −(N/2),. . . , −3, −2, −1. For Option 5 with an IFFT size of 8, the STF can bedefined in the frequency domain as:

Option 5: PAR=3.0103 dB

[0 0 −1 0 0 0 −1 0]  [0 0 1 0 0 0 1 0].

For Option 4, the STF can be defined in the frequency domain as:

Option 4: PAR=4.3983 dB

[0 0 −1 0 −1 0 1 0 0 0 1 0 −1 0 −1 0] [0 0 −1 0 1 0 1 0 0 0 1 0 1 0 −10] [0 0 1 0 −1 0 −1 0 0 0 −1 0 −1 0 1 0] [0 0 1 0 1 0 −1 0 0 0 −1 0 1 01  0].

For Option 3, the STF can be defined in the frequency domain as:

Option 3: PAR=4.3983 dB

[0 0 0 0 −1 0 0 0 −1 0 0   0 1 0 0 0 0 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0][0 0 0 0 −1 0 0 0 1 0 0   0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0] [00 0 0 1 0 0 0 −1 0 0   0 −1 0 0 0 0 0 0 0 −1 0 0 0 −1 0 0 0 1 0 0 0] [00 0 0 1 0 0 0 1 0 0   0 −1 0 0 0 0 0 0 0 −1 0 0 0 1 0 0 0 1 0 0  0].

For Option 2, the STF can be defined in the frequency domain as:

Option 2: PAR=5.0685 dB

[0   0 0 0 −1 0 0 0 −1 0 0 0 −1 0 0 0 −1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 00 0 0 0 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 −1 0 0 0 −1 0 0   0][0   0 0 0 −1 0 0 0 1 0 0 0 −1 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 0 0 0 0 00 0 0 0 0 0 0 −1 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 1 0 0 0 −1 0 0   0] [0  0 0 0 1 0 0 0 −1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 00 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 1 0 0 0 −1 0 0 0 1 0 0   0] [0   0 0 01 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 0 0 0 0 0 0 0 0 0 0 00 −1 0 0 0 −1 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 1 0 0   0].

These sequences are given in Matlab format. For Option 5, the first 0represents the DC tone, which is not used. The next three subcarriersare 1, 2, and 3. In general, if there are N subcarriers, the Matlabsubcarrier numbering is 0, 1, 2, 3, . . . , (N/2)−1 followed by −(N/2),. . . , −3, −2, −1. For Option 1, the STF can be defined in thefrequency domain as:

Option 1: PAR=4.4012 dB

[0 0 0 0 −1 0 0 0 −1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 1 0 0 0 −1 0 0 0 −10 0 0 −1 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 −1 0 0 01 0 0 0 −1 0 0 0 −1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0] [0 0 0 0 −1 0 0 0 10 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 −1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 00 1 0 0 0 −1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 −1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 −1 0 0 01 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0] [0 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 −10 0 0 1 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 1 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 −1 0 0 01 0 0 0 1 0 0 0 −1 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 −1 00 0 1 0 0 0] [0 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 01 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 −1 0 0 0 −1 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 −1 0 0 0 −1 0 0 0 −1 0 0 0 1 0 0 0 1 00 0 1 0 0 0 −1 0 0 0 1 0 0 0 1 0 0 0 −1 0 0 0 1 0 0 0 1 0 0 0].

In at least one embodiment, the STF can be designed using rotated QPSKsymbols. In another embodiment, the STF can be designed using rotatedBPSK symbols. By having freedom in the design of the sequences, the PARcan be lowered for Option 1 and 2 easily on a case-by-case basis.

These sequences are given in Matlab format. For Option 5, the first 0represents the DC tone, which is not used. The next three subcarriersare 1, 2, and 3. In general, if there are N subcarriers, the Matlabsubcarrier numbering is 0, 1, 2, 3, . . . , (N/2)−1 followed by −(N/2),. . . , −3, −2, −1. An example of STFs using QPSK are:

Option 5: PAR=3.0103 dB

[0 0 −j 0 0 0 j 0] [0 0 j 0 0 0 −j 0];

Option 4: PAR=4.3983 dB

In addition to the 4 sequences for BPSK,

[0 0 −j 0 −1 0 −j 0 0 0 j 0 −1 0 j 0] [0 0 −j 0 1 0 −j 0 0 0 j 0 1 0 j0] [0 0 j 0 −1 0 j 0 0 0 −j 0 −1 0 −j 0] [0 0 j 0 1 0 j 0 0 0 −j 0 1 0−j 0];

Option 3: PAR=4.3983 dB

[0 0 0 0 −j 0 0 0 −1 0 0 0 −j 0 0 0 0 0 0 0 j 0 0 0 −1 0 0 0 j 0 0 0] [00 0 0 −j 0 0 0 1 0 0 0 −j 0 0 0 0 0 0 0 j 0 0 0 1 0 0 0 j 0 0 0] [0 0 00 j 0 0 0 −1 0 0 0 j 0 0 0 0 0 0 0 −j 0 0 0 −1 0 0 0 −j 0 0 0] [0 0 0 0j 0 0 0 1 0 0 0 j 0 0 0 0 0 0 0 −j 0 0 0 1 0 0 0 −j 0 0 0];

Option 2: PAR=4.2346 dB

[0 0 0 0 −1 0 0 0 −j 0 0 0 1 0 0 0 j 0 0 0 1 0 0 0 −j 0 0 0 0 0 0 0 0 00 0 0 0 0 0 j 0 0 0 1 0 0 0 −j 0 0 0 1 0 0 0 j 0 0 0 −1 0 0 0] [0 0 0 0−1 0 0 0 j 0 0 0 1 0 0 0 −j 0 0 0 1 0 0 0 j 0 0 0 0 0 0 0 0 0 0 0 0 0 00 −j 0 0 0 1 0 0 0 j 0 0 0 1 0 0 0 −j 0 0 0 −1 0 0 0] [0 0 0 0 1 0 0 0−j 0 0 0 −1 0 0 0 j 0 0 0 −1 0 0 0 −j 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 j 00 0 −1 0 0 0 −j 0 0 0 −1 0 0 0 j 0 0 0 1 0 0 0] [0 0 0 0 1 0 0 0 j 0 0 0−1 0 0 0 −j 0 0 0 −1 0 0 0 j 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 −j 0 0 0 −1 00 0 j 0 0 0 −1 0 0 0 −j 0 0 0 1 0 0 0] [0 0 0 0 −j 0 0 0 −j 0 0 0 −j 0 00 −j 0 0 0 j 0 0 0 −j 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 j 0 0 0 −j 0 0 0 j 00 0 j 0 0 0 j 0 0 0 j 0 0 0] [0 0 0 0 −j 0 0 0 j 0 0 0 −j 0 0 0 j 0 0 0j 0 0 0 j 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 −j 0 0 0 −j 0 0 0 −j 0 0 0 j 0 00 −j 0 0 0 j 0 0 0] [0 0 0 0 j 0 0 0 −j 0 0 0 j 0 0 0 −j 0 0 0 −j 0 0 0−j 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 j 0 0 0 j 0 0 0 j 0 0 0 −j 0 0 0 j 0 00 −j 0 0 0] [0 0 0 0 j 0 0 0 j 0 0 0 j 0 0 0 j 0 0 0 −j 0 0 0 j 0 0 0 00 0 0 0 0 0 0 0 0 0 0 −j 0 0 0 j 0 0 0 −j 0 0 0 −j 0 0 0 −j 0 0 0 −j 0 00];and

Option 1: PAR=3.7261 dB

[0 0 0 0 j 0 0 0 −j 0 0 0 −j 0 0 0 j 0 0 0 j 0 0 0 −j 0 0 0 j 0 0 0 −j 00 0 j 0 0 0 j 0 0 0 j 0 0 0 j 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 −j 0 0 0 −j 0 0 0 −j 0 0 0 −j 0 0 0 j 0 0 0 −j 0 0 0j 0 0 0 −j 0 0 0 −j 0 0 0 j 0 0 0 j 0 0 0 −j 0 0 0].

These sequences are given in Matlab format. For Option 5, the first 0represents the DC tone, which is not used. The next three subcarriersare 1, 2, and 3. In general, if there are N subcarriers, the Matlabsubcarrier numbering is 0, 1, 2, 3, . . . , (N/2)−1 followed by −(N/2),. . . , −3, −2, −1. Some examples of LTFs using a rotated BPSK are:

Option 5: PAR=4.3983 dB

[0 −1 −1 1 0 1 −1 −1] [0 −1 1 1 0 1 1 −1] [0 1 −1 −1 0 −1 −1 1] [0 1 1−1 0 −1 1 1];

Option 4: PAR=4.1017 dB

[0 −1 −1 −1 1 1 −1 1 0 1 −1 1 1 −1 −1 −1] [0 −1 1 −1 −1 1 1 1 0 1 1 1 −1−1 1 −1] [0 1 −1 1 1 −1 −1 −1 0 −1 −1 −1 1 1 −1 1] [0 1 1 1 −1 −1 1 −1 0−1 1 −1 −1 1 1 1];

Option 3: PAR=4.1538 dB

[0 −1 −1 −1 −1 −1 1 −1 1 1 1 −1 −1 1 0 0 0 0 0 1 −1 −1 1 1 1 −1 1 −1 −1−1 −1 −1] [0 −1 1 −1 1 −1 −1 −1 −1 1 −1 −1 1 1 0 0 0 0 0 1 1 −1 −1 1 −1−1 −1 −1 1 −1 1 −1] [0 1 −1 1 −1 1 1 1 1 −1 1 1 −1 −1 0 0 0 0 0 −1 −1 11 −1 1 1 1 1 −1 1 −1 1] [0 1 1 1 1 1 −1 1 −1 −1 −1 1 1 −1 0 0 0 0 0 −1 11 −1 −1 −1 1 −1 1 1 1 1 1];

Option 2: PAR=4.4236 dB

[0 −1 −1 −1 −1 1 −1 1 −1 1 1 −1 1 1 −1 −1 1 −1 −1 −1 1 1 1 −1 −1 −1 −1 00 0 0 0 0 0 0 0 0 0 −1 −1 −1 −1 1 1 1 −1 −1 −1 1 −1 −1 1 1 −1 1 1 −1 1−1 1 −1 −1 −1 −1];andOption 1 (100 data sub-carriers): PAR=5.0478 dB

[0 1 1 −1 −1 1 1 −1 1 1 1 −1 1 1 −1 1 −1 1 −1 −1 −1 −1 −1 1 1 1 1 −1 −1−1 1 −1 1 −1 −1 1 1 1 1 −1 −1 −1 1 −1 −1 −1 1 −1 −1 −1 −1 1 1 −1 1 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 −1 1 1 −1 −1 −1 −1 1 −1 −1 −1 1 −1 −1−1 1 1 1 1 −1 −1 1 −1 1 −1 −1 −1 1 1 1 1 −1 −1 −1 −1 −1 1 −1 1 −1 1 1 −11 1 1 −1 1 1 −1 −1 1 1]Option 1 (96 data sub-carriers): PAR=5.2695 dB

[0 1 −1 −1 1 1 −1 −1 1 1 −1 1 1 1 1 −1 1 −1 −1 −1 −1 −1 −1 1 1 1 1 1 −1−1 1 −1 1 1 1 −1 −1 −1 −1 1 1 −1 −1 −1 −1 1 −1 −1 −1 −1 1 −1 −1 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 −1 −1 1 −1 −1 −1 −1 1 −1 −1 −1 −11 1 −1 −1 −1 −1 1 1 1 −1 1 −1 −1 1 1 1 1 1 −1 −1 −1 −1 −1 −1 1 −1 1 1 11 −1 1 1 −1 −1 1 1 −1 −1 1].

In at least one embodiment, a scaling factor is included to match theenergy in the STF to the energy in the data symbols. For option 5, theSTF can be scaled by sqrt(6/2) if there are 6 pilot+ data subcarriersused for the data OFDM symbols while two sub-carriers are used for STF.Alternatively, the sub-carriers are scaled down in the data OFDM symbolsto match the energy in the STF. Some examples of STFs including scalingfactors are:

STF_freq(Option-1)=sqrt(104/24)*[0,zeros(1,3),j,zeros(1,3),−j,zeros(1,3),j,zeros(1,3),j,zeros(1,3),j,zeros(1,3),−j,zeros(1,3),j,zeros(1,3),−j,zeros(1,3),j,zeros(1,3),j,zeros(1,3),j,zeros(1,3),j,zeros(1,31),−j,zeros(1,3),−j,zeros(1,3),−j,zeros(1,3),−j,zeros(1,3),j,zeros(1,3),−j,zeros(1,3),j,zeros(1,3),−j,zeros(1,3),−j,zeros(1,3),j,zeros(1,3),j,zeros(1,3),−j,zeros(1, 3)];STF_freq(Option-2)=sqrt(52/12)*[0,zeros(1,3),−1,zeros(1,3),−j,zeros(1,3),1,zeros(1,3),j,zeros(1,3),1,zeros(1,3),−j,zeros(1,15),j,zeros(1,3),1,zeros(1,3),−j,zeros(1,3),1,zeros(1,3),j,zeros(1,3),−1,zeros(1,3)];STF_freq(Option-3)=sqrt(26/6)*[0,zeros(1,3),−j,zeros(1,3),−1,zeros(1,3),−j,zeros(1,3),0,zeros(1,3),j,zeros(1,3),−1,zeros(1,3), j,zeros(1,3)];STF_freq(Option-4)=sqrt(14/6)*[0,0,−j,0,−1,0,−j,0,0,0,j,0,−1,0,j,0]; andSTF_freq(Option-5)=sqrt(6/2)*[0,0,−j,0,0,0,j,0].

These sequences are given in Matlab format. For Option 5, the first 0represents the DC tone, which is not used. The next three subcarriersare 1, 2, and 3. In general, if there are N subcarriers, the Matlabsubcarrier numbering is 0, 1, 2, 3, . . . , (N/2)−1 followed by −(N/2),. . . , −3, −2, −1. Some examples of LTFs are:

LTF_freq(Option-1)=[0, 1,−1,−1, 1, 1,−1,−1, 1, 1,−1, 1, 1, 1, 1,−1,1,−1,−1,−1,−1,−1,−1, 1, 1, 1, 1, 1,−1,−1, 1,−1, 1, 1, 1,−1,−1,−1,−1, 1,1,−1,−1,−1,−1, 1,−1,−1,−1,−1, 1,−1,−1,zeros(1,23), −1,−1, 1,−1,−1,−1,−1,1,−1,−1,−1,−1, 1, 1,−1,−1,−1,−1, 1, 1, 1,−1, 1,−1,−1, 1, 1, 1, 1,1,−1,−1,−1,−1,−1,−1, 1,−1, 1, 1, 1, 1,−1, 1, 1,−1,−1, 1, 1,−1,−1, 1];LTF_freq(Option-2)=[0,−1,−1,−1,−1, 1,−1, 1,−1, 1, 1,−1, 1, 1,−1,−1,1,−1,−1,−1, 1, 1, 1,−1,−1 −1,−1, zeros(1,11),−1,−1,−1,−1, 1, 1,1,−1,−1,−1, 1,−1,−1, 1, 1,−1, 1, 1,−1, 1,−1, 1,−1,−1,−1,−1];LTF_freq(Option-3)=[0,−1,−1,−1,−1,−1, 1,−1, 1, 1, 1,−1,−1, 1,zeros(1,5), 1,−1,−1, 1, 1, 1,−1, 1,−1, −1,1,−1,−1];LTF_freq(Option-4)=[0,−1,−1,−1,1,1,−1,1,zeros(1,1),1,−1,1,1,−1,−1,−1];andLTF_freq(Option-5)=[0,−1,−1,1, zeros(1,1),1,−1,−1].

An alternative example of a LTF using 100 data sub-carriers is:

LTF_freq(Option-1 alternative)=[0, 1, 1,−1,−1, 1, 1,−1, 1, 1, 1,−1, 1,1,−1, 1,−1, 1,−1,−1,−1,−1,−1, 1, 1, 1, 1,−1,−1,−1, 1,−1, 1,−1,−1, 1, 1,1, 1,−1,−1,−1, 1,−1,−1,−1, 1,−1,−1,−1,−1, 1, 1,−1, 1,zeros(1,19), 1,−1,1, 1,−1,−1,−1,−1, 1,−1,−1,−1, 1,−1,−1,−1, 1, 1, 1, 1,−1,−1, 1,−1,1,−1,−1,−1, 1, 1, 1, 1,−1,−1,−1,−1,−1, 1,−1, 1,−1, 1, 1,−1, 1, 1, 1,−1,1, 1,−1,−1, 1, 1].

In some embodiments, the preamble can be constructed to enable efficientboundary detection of the start of the OFDM packet. For example, FIG. 6shows that a negation is applied for the last repetition in the STF. Inat least one embodiment, the last repetition of a group of bits in thefinal STF is negated at the transmitter, and the receiver can use thisinformation to determine when the sign change takes place so that theend of the STF can be determined accurately. Specifically, the output ofa correlator shows a characteristic pattern at the boundary of the STFand LTF. In various embodiments, the last 2, 3, or N repetitions arenegated. When cross-correlation is used (correlating against a knownsequence), the transition that occurs from z to −z can be found bymonitoring for a phase change of 180 degrees (in the noiseless case) inthe correlator output. In FIG. 6, the “z” represents one group of bitsrepeated in the STF, which is itself repeated. In another embodiment,the entire final repeated STF is negated. In other embodiments, the sizeof the bits that are negated varies. Returning to FIG. 6, there are twoOFDM symbols because the cyclic prefix is 1/4 of the useful part of theOFDM symbol, and there is a repetition of 4 within the OFDM symbol dueto the structure of the STF. Because the time-domain representation ofthe STF is real, any negative time-domain values for the last repetitionare changed to positive and any positive time-domain values are changedto negative. In another embodiment the STF is complex, so the both thereal and imaginary parts are negated for the last repetition within thelast STF.

FIG. 7 illustrates a method of generating STFs and LTFs beginning at 702and ending at 714. While at least one embodiment is illustrated, themethod 700 can comprise any step described above in various embodiments.At 704, a first plurality of symbols comprising real portions andcomplex portions is received. At 706, conjugate symmetry is applied tothe first plurality of symbols, thus producing a second plurality ofsymbols comprising real portions and no complex portions. At 708, thesecond plurality of symbols is transformed using an inverse fast Fouriertransform, thus producing a third plurality of symbols. In at least oneembodiment, the second plurality of symbols is interpolated. At 710, ashort training field is generated comprising at least one real portionof the third plurality of symbols. At 712, a long training field isgenerated comprising at least one real portion of the third plurality ofsymbols. At 714, the short training field and long training field aretransmitted in a wireless personal area network. In at least oneembodiment, power is reduced to logic responsible for complex symbolprocessing. A final repetition of a group of bits is negated in at leastone embodiment. Preferably, the last portion of the STF is negated. Inan alternative embodiment the block 706 is omitted so that the STF andLTF are complex.

The system described above may be implemented on a particular machinewith sufficient processing power, memory resources, and networkthroughput capability to handle the necessary workload placed upon it.FIG. 8 illustrates a particular machine 880 suitable for implementingone or more embodiments disclosed herein. The computer system 880includes one or more processors 882 (which may be referred to as acentral processor unit or CPU) that is in communication with amachine-readable medium 887. The machine-readable medium 887 maycomprise memory devices including secondary storage 884, read onlymemory (ROM) 886, and random access memory (RAM) 888. The processor isfurther in communication with input/output (I/O) 890 devices and networkconnectivity devices 892. The processor may be implemented as one ormore CPU chips.

The secondary storage 884 is typically comprised of one or more diskdrives, tape drives, or optical discs and is used for non-volatilestorage of data and as an over-flow data storage device if RAM 888 isnot large enough to hold all working data. Secondary storage 884 may beused to store programs and instructions 889 that are loaded into RAM 888when such programs are selected for execution. The ROM 886 is used tostore instructions 889 and perhaps data, which are read during programexecution. ROM 886 is a non-volatile memory device that typically has asmall memory capacity relative to the larger memory capacity ofsecondary storage. The RAM 888 is used to store volatile data andperhaps to store instructions 889. Access to both ROM 886 and RAM 888 istypically faster than to secondary storage 884.

I/O 890 devices may include printers, video monitors, liquid crystaldisplays (LCDs), touch screen displays, keyboards, keypads, switches,dials, mice, track balls, voice recognizers, card readers, paper tapereaders, or other well-known input devices. The network connectivitydevices 892 may take the form of modems, modem banks, ethernet cards,universal serial bus (USB) interface cards, serial interfaces, tokenring cards, fiber distributed data interface (FDDI) cards, wirelesslocal area network (WLAN) cards, radio transceiver cards such as codedivision multiple access (CDMA) and/or global system for mobilecommunications (GSM) radio transceiver cards, and other well-knownnetwork devices. These network connectivity 892 devices may enable theprocessor 882 to communicate with an Internet or one or more intranets.With such a network connection, the processor 882 may receiveinformation from the network, or may output information to the networkin the course of performing the above-described method steps. Suchinformation, which is often represented as a sequence of instructions889 to be executed using processor 882, may be received from and outputto the network, for example, in the form of a computer data signalembodied in a carrier wave

Such information, which may include data or instructions 889 to beexecuted using processor 882 for example, may be received from andoutput to the network, for example, in the form of a computer databaseband signal or signal embodied in a carrier wave. The basebandsignal or signal embodied in the carrier wave generated by the networkconnectivity 892 devices may propagate in or on the surface ofelectrical conductors, in coaxial cables, in waveguides, in opticalmedia, for example optical fiber, or in the air or free space. Theinformation contained in the baseband signal or signal embedded in thecarrier wave may be ordered according to different sequences, as may bedesirable for either processing or generating the information ortransmitting or receiving the information. The baseband signal or signalembedded in the carrier wave, or other types of signals currently usedor hereafter developed, referred to herein as the transmission medium,may be generated according to several methods well known to one skilledin the art.

The processor 882 executes instructions 889, codes, computer programs,scripts which it accesses from hard disk, floppy disk, optical disc(these various disk based systems may all be considered secondarystorage 884), ROM 886, RAM 888, or the network connectivity devices 892.

In an alternative embodiment the system may be implemented in anapplication specific integrated circuit (“ASIC”) comprising logicconfigured to perform any action described in this disclosure withcorresponding and appropriate inputs and outputs or a digital signalprocessor (“DSP”).

The above disclosure is meant to be illustrative of the principles andvarious embodiment of the present invention. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. Additionally, audio or visualalerts may be triggered upon successful completion of any actiondescribed herein, upon unsuccessful actions described herein, and uponerrors. Also, the order of the actions shown in FIG. 7 can be variedfrom order shown, and two or more of the actions may be performedconcurrently. It is intended that the following claims be interpreted toembrace all variations and modifications.

What is claimed is:
 1. A communication device comprising: transmitcircuitry; an antenna coupled to the transmit circuitry; a processor;and a non-transitory machine-readable storage medium comprisingexecutable instructions that, when executed, cause the processor to:generate a first packet that includes a synchronization header, a packetheader, and a packet payload, wherein the synchronization header includea short training field (STF) and a long training field (LTF), whereinthe STF and LTF are arranged directly adjacent to one another within thesynchronization header; and cause the transmit circuitry to transmit thefirst packet over a network using the antenna.
 2. The communicationdevice of claim 1, wherein the LTF includes a real portion of a timedomain sequence corresponding to a second packet received by thecommunication device prior to generation of the first packet.
 3. Thecommunication device of claim 2, wherein the time domain sequence isproduced by performing an inverse Fourier transform on a frequencydomain signal corresponding to the second packet.
 4. The communicationdevice of claim 1, wherein the STF, when represented in a frequencydomain, includes the values [0, 0, −1, 0, 1, 0, −1, 0, 0, 0, 1, 0, 1, 0,1, 0] for tones [0, 1, 2, 3, 4, 5, 6, 7, −8, −7, −6, −5, −4, −3, −2,−1], respectively, and the values of 1 and −1 are adjustable based on ascaling factor.
 5. The communication device of claim 4, wherein thescaling factor is sqrt(14/6).
 6. The communication device of claim 1,wherein the STF, when represented in a frequency domain, includes thevalues [0, 0, 0, 0, −1, 0, 0, 0, 1, 0, 0, 0, −1, 0, 0, 0, 0, 0, 0, 0, 1,0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0] for tones [0, 1, 2, 3, 4, 5, 6, 7, 8,9, 10, 11, 12, 13, 14, 15, −16, −15, −14, −13, −12, −11, −10, −9, −8,−7, −6, −5, −4, −3, −2, −1], respectively, and the values of 1 and −1are adjustable based on a scaling factor.
 7. The communication device ofclaim 6, wherein the scaling factor is sqrt(26/6).
 8. The communicationdevice of claim 1, wherein the STF, when represented in a frequencydomain, includes the values [0, 0, 0, 0, 1, 0, 0, 0, −1, 0, 0, 0, 1, 0,0, 0, 1, 0, 0, 0, −1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,0, 0, −1, 0, 0, 0, −1, 0, 0, 0, −1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1,0, 0, 0] for tones [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, −32,−31, −30, −29, −28, −27, −26, −25, −24, −23, −22, −21, −20, −19, −18,−17, −16, −15, −14, −13, −12, −11, −10, −9, −8, −7, −6, −5, −4, −3, −2,−1], respectively, and the values of 1 and −1 are adjustable based on ascaling factor.
 9. The communication device of claim 8, wherein thescaling factor is sqrt(52/12).
 10. The communication device of claim 1,wherein the STF, when represented in a frequency domain, includes thevalues [0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, −1, 0, 0, 0, 0,0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, −1, 0, 0, 0, 0,0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, −1, 0, 0, 0, 0, 0, 0, 0, −1, 0, 0,0, 0, 0, 0, 0, −1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0,0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0] for tones [0, 1, 2, 3, 4, 5, 6,7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43,44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61,62, 63, −64, −63, −62, −61, −60, −59, −58, −57, −56, −55, −54, −53, −52,−51, −50, −49, −48, −47, −46, −45, −44, −43, −42, −41, −40, −39, −38,−37, −36, −35, −34, −33, −32, −31, −30, −29, −28, −27, −26, −25, −24,−23, −22, −21, −20, −19, −18, −17, −16, −15, −14, −13, −12, −11, −10,−9, −8, −7, −6, −5, −4, −3, −2, −1], respectively, and the values of 1and −1 are adjustable based on a scaling factor.
 11. The communicationdevice of claim 10, wherein the scaling factor is sqrt(104/12).
 12. Thecommunication device of claim 1, wherein the LTF, when represented in afrequency domain, includes the values [0, −1, 1, 1, 1, −1, −1, −1, 0, 1,−1, 1, 1, −1, 1, 1] for tones [0, 1, 2, 3, 4, 5, 6, 7, −8, −7, −6, −5,−4, −3, −2, −1], respectively.
 13. The communication device of claim 1,wherein the LTF, when represented in a frequency domain, includes thevalues: [0, −1, −1, 1, −1, 1, 1, −1, −1, 1, 1, −1, −1, 1, 0, 0, 0, 0, 0,1, −1, 1, −1, 1, 1, 1, 1, 1, 1, 1, 1, −1] for tones [0, 1, 2, 3, 4, 5,6, 7, 8, 9, 10, 11, 12, 13, 14, 15, −16, −15, −14, −13, −12, −11, −10,−9, −8, −7, −6, −5, −4, −3, −2, −1], respectively.
 14. The communicationdevice of claim 1, wherein the LTF, when represented in a frequencydomain, includes the values [0, 1, −1, 1, 1, −1, 1, −1, −1, 1, −1, 1, 1,−1, −1, 1, 1, −1, −1, −1, −1, −1, 1, −1, −1, −1, 1, 0, 0, 0, 0, 0, 0, 0,0, 0, 0, 0, −1, −1, −1, −1, 1, 1, 1, −1, 1, −1, 1, −1, 1, 1, −1, −1, −1,1, 1, −1, 1, 1, 1, −1, −1, −1] for tones [0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27,28, 29, 30, 31, −32, −31, −30, −29, −28, −27, −26, −25, −24, −23, −22,−21, −20, −19, −18, −17, −16, −15, −14, −13, −12, −11, −10, −9, −8, −7,−6, −5, −4, −3, −2, −1], respectively.
 15. The communication device ofclaim 1, wherein the LTF, when represented in a frequency domain,includes the values [0, 1, −1, 1, −1, 1, 1, −1, −1, 1, −1, 1, 1, 1, 1,−1, 1, 1, 1, 1, 1, −1, 1, −1, 1, −1, 1, −1, 1, 1, −1, 1, −1, −1, −1, 1,1, 1, 1, 1, 1, −1, −1, −1, −1, −1, −1, 1, −1, 1, 1, −1, 1, 0, 0, 0, 0,0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, −1, 1, 1, −1,−1, −1, −1, 1, 1, −1, −1, 1, 1, 1, −1, −1, 1, 1, −1, −1, −1, −1, −1, 1,1, −1, −1, −1, −1, −1, 1, 1, −1, 1, −1, −1, 1, −1, 1, 1, 1, 1, −1, −1,1, 1, −1, 1, 1, −1, 1, 1] for tones [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46,47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, −64,−63, −62, −61, −60, −59, −58, −57, −56, −55, −54, −53, −52, −51, −50,−49, −48, −47, −46, −45, −44, −43, −42, −41, −40, −39, −38, −37, −36,−35, −34, −33, −32, −31, −30, −29, −28, −27, −26, −25, −24, −23, −22,−21, −20, −19, −18, −17, −16, −15, −14, −13, −12, −11, −10, −9, −8, −7,−6, −5, −4, −3, −2, −1], respectively.